1. Technical Field
The present invention relates to conveyance devices that convey sheet media stored in a roll, and relates more particularly to media conveyance devices that can perform a reversing operation in a short time, convey media accurately in reverse, improve throughput, and prevent paper jams.
2. Related Art
Receipt printers and other devices that process sheet media (such as paper) stored in a roll have a device for conveying the media to a processing position. The conveyance device usually has an upstream roller that feeds the media from the roll to the conveyance path, and a downstream roller that supplies the fed media to the processing position, and the media is conveyed by driving these rollers.
The media must be conveyed in reverse after finishing one job in order to prepare for the next job or for maintenance, for example, in printers and other devices having such a conveyance device. Reversing the media involves an operation that rotates the media stored in a roll on the roll axis and rewinds the media to a specific position. The reversing operation is also conventionally performed with the upstream roller applying pressure to the media, that is, with tension applied between the upstream roller and the media roll.
Related to this technology, Japanese Unexamined Patent Appl. Pub. JP-A-H06-144664 is directed to a method of correcting bias in roll paper supplied to a plotter. This method applies tension to the roll paper while conveying the paper over the recording surface, and then allows the fed roll paper to sag while winding it around the paper roll. Slack in the roll paper is then removed by stopping reverse rotation of the drive roller and the paper roll in the last step of winding the paper around the paper roll. These steps repeat several times to remove the bias. Stopping reverse rotation of the paper roll without delay at this time is also described.
However, if a control method that tracks a predetermined deceleration curve (a speed curve over time) is used in the conventional reversing operation described above as the method of slowing and stopping rotation of the roll media when stopping operation, unstable behavior, such as re-acceleration while slowing, can occur due to inertia changing with the roll diameter. This can then result in an increase in the time or distance needed to stop. In addition, because tension is applied to the medium between the upstream roller and the media roll, if the direction or position of the media shifts on the media roll side, that shift gets transferred to the upstream roller located downstream therefrom or to the downstream side of the upstream roller. Because this shift occurs easily particularly when the roll diameter is large and is amplified with propagation downstream, the media can become jammed in the structural members of the conveyance path when the shift is great. If operation stops when the media has shifted, media processing will also be shifted when the media is then conveyed forward for processing, and process quality will drop.
Furthermore, while stopping reverse rotation of the paper roll without delay is described in JP-A-H06-144664, a specific method is not disclosed, and what to do about movement of the paper due to roll paper inertia is not addressed. As a result, when the paper shifts from the correct position, time is required to correct the position. There is also a problem with the precision of the stopping position because there is no awareness of the stopping position in the conveyance direction and the inertia of the paper roll when driving stops is not considered.